Exactly.
The orange car did exactly what they were supposed to do.
They went into the inside lane on entering the roundabout because they were taking an exit after 12 o'clock.
They started to move over into the outside lane after passing the exit where OP entered the roundabout, in good time to avoid suddenly needing to cut in last minute and potentially cut someone up.
They literally had no option but to move into that outside lane to get off the roundabout, whichever lane of the exit road they were planning to use, because that's how roads work. Cars can't fly.
OP seems to think they should have been indicating BEFORE she joined the roundabout, so she'd know they were going to switch lane. No. That would have made other drivers think the orange car was going to turn off at the exit where OP entered, and could have caused an accident.
OP is completely wrong - pulling out when she did basically blocked the orange car from taking the line they were intending to take, meaning that the orange car would have had to stamp on the brakes as she cut them up or suddenly drive around her, altering course and potentially cutting up another car on the inside lane, to get into the right-hand lane of the exit road. And she's surprised they gave her the finger.
The other driver was completely correct. OP forced them to take evasive action, which is a major on the driving test. She also failed to give way to the right on a roundabout, another major. She also failed to observe what the orange car was very clearly doing, another major. How does this woman have a driving licence?